It has previously been suggested to use a spring loaded bladder as an ink reservoir or a foam filled ink reservoir for a portable or disposable thermal ink jet cartridge to contain the ink during both shipping and use. Both the spring loaded bladders and the foam filled reservoirs have not had a high volume efficiency because of the back pressure mechanism that each has contained.
Neither arrangement has been easily refilled. The spring loaded bladder has been sealed and maintained at a negative pressure so that any refilling of the bladder has been difficult since it is necessary for the bladder to continue to have the negative pressure therein.
In a foam filled reservoir, as the ink is used, air pockets form in the ink and the foam surfaces de-wet. The foam can be refilled and used multiple times, but the number of air pockets in the foam increases with each refilling so that the foam eventually cannot be refilled.
It has previously been suggested in U.S. Pat. No. 4,677,447 to Nielsen to employ a check valve to contain the ink during shipping as well as use. The check valve allows ink to flow from the reservoir into a small cavity adjacent nozzles of a thermal ink jet printhead and from which the ink flows into the nozzles. The check valve has been preloaded to establish a valve opening pressure in excess of the hydrostatic pressure resulting at least from the maximum depth of ink in the reservoir. The check valve prevents depriming of the small cavity so that neither the introduction of foam in the reservoir nor the use of a spring loaded elastic bladder as the reservoir is necessary to prevent leakage through the nozzles by gravity.
However, the check valve of the aforesaid Nielsen Patent is not capable of preventing air bubbles, which are trapped within the small cavity and expand and contract due to pressure and/or temperature variations, from pumping ink out of the small cavity of the aforesaid Nielsen Patent. Thus, ink leakage could occur through the nozzles by an expanding and contracting air bubble pumping ink out of the small cavity to the nozzles.
If the check valve of the aforesaid Nielsen Patent should allow too much ink to flow into the small cavity, the pressure would increase in the small cavity so that there would be leakage of the ink through the nozzles. Therefore, the check valve of the aforesaid Nielsen Patent does not satisfactorily solve all of the problems causing ink leakage.